Mobile working machines are also used in work environments characterized by steep uphill and downhill inclinations. During this, transport vehicles are loaded by mobile working machines, for example even on an inclined surface. In most cases transport vehicles are loaded by means of wheel loaders, which comprise a corresponding working hydraulic system for the purpose. During the loading process, for example a scoop filled with the material to be loaded has to be raised in order to reach a load container of a transport vehicle at a certain height, into which the material is discharged. Loading involves continual travel direction changes along with low travel speeds, in order to reach in each case the optimum unloading position for the wheel loader.
In working machines a travel direction is often specified with the help of a so-termed steering column switch, which has at least three detent positions, namely for forward driving, driving in reverse and for a so-termed neutral operating condition of the vehicle drive-train of such a working machine. When the neutral operating condition is called for, the power flow between the drive engine and the drive output of a mobile working machine is interrupted.
As a rule, the detent position corresponding to the neutral operating condition is located between the detent positions for driving forward and driving in reverse. As a result, actuation of the steering column switch starting from the detent position for forward or reverse driving, in the direction toward the detent position for reverse or forward driving, respectively, has to pass through the detent position of the steering column switch for the neutral operating condition. Below a defined actuation speed of the steering column switch the dwell-time of the steering column switch in the detent position for the neutral operating condition is consequently too long, so that, whether he wants to or not, the driver will emit a command for the neutral operating condition to a transmission of the vehicle drive-train of a mobile working machine and the power flow between the drive engine and the drive output of the mobile working machine is interrupted in the area of the transmission by a corresponding actuation of the transmission.
If such a neutral request or command to set the neutral operating condition of a vehicle drive-train of a mobile working machine occurs while the working machine is on an inclined surface, the vehicle or mobile working machine may roll away, and if this happens when the working hydraulic system is in the raised position with the scoop full, the working performance of the mobile working machine is impeded, which is therefore undesirable.
From DE 10 2013 200 392 A1 a method is known for the operation of a vehicle drive-train having a drive engine with a continuously power-branched transmission and with a drive output. The transmission consists of a reversing gear unit, a planetary gearset and a range group. The reversing gear unit comprises reversing clutches with which the rotational direction of the transmission is switched and which, together with the range clutches, establish the power flow between the drive engine and the drive output. In the area of the planetary gearset the force or power flow from the drive engine is divided into a mechanical and a hydrostatic power fraction. By way of the range group the maximum drive output rotational speed can be increased and the power flow is established between the variator and the drive output and also between the drive output and the reversing gear unit.
When a command to engage the neutral operating condition is issued, both the reversing clutches of the reversing gear unit and the shifting elements of the range group are changed to the open operating condition, in order to interrupt the power flow in the area between the drive engine and the transmission input and also between the variator and the drive output.
However, this procedure leads disadvantageously to the result that when it is on an incline and especially if an unwanted command to engage the neutral operating condition occurs, a mobile working machine built with the continuously power-branched transmission, will roll away to an undesired extent unless at the same time the driver actuates a service brake of the working machine.